A wireless transceiver includes a baseband modem and a Radio Frequency Integrated Circuit (RFIC) to physically send and receive signals. The RFIC transmits a baseband signal using radio waves in a wireless communication environment, and forwards a signal received via an antenna to the baseband modem without distortion. Particularly, as wireless communication standards evolve, a transmit circuit of the RFIC advances to linearly amplify and process more complicated signals. In terms of performance and efficiency, the signal processing of the RFIC requires minimum current consumption.
Wideband Code Division Multiple Access (WCDMA), being a 3rd generation (3G) communication standard, and Long Term Evolution (LTE), being a 4th generation (4G) communication standard, require a dynamic range of an output power. To satisfy the above-described requirements of the communication standard, the gain of the RFIC should be controlled finely through certain steps beyond 80 dB. Typically, to meet the dynamic range over 80 dB, an analog baseband circuit and a Radio Frequency (RF) Variable Gain Amplifier (VGA) are designed to vary the gain.
The gain variation at the analog baseband stage can change a Direct Current (DC) offset in size. The DC offset can appear as Local Oscillator (LO) leakage at the transmit output stage and thus Error Vector Magnitude (EVM) performance can be degraded. Hence, the change of the DC offset size according to the gain variation at the analog baseband stage needs to be compensated through calibration. As a load of the analog baseband stage for the desired dynamic range increases, a calibration point required for the DC offset increases in number, which extends the calibration time. To obtain the dynamic range of the gain, it is advantageous to minimize the load of the analog baseband stage and to increase the load of the RF stage for the dynamic range of the gain. In this regard, it is general to design a multi-stage (two or more stages) RF VGA structure for processing the dynamic range over 60 dB.
An amplifier of two or more stages can relatively easily obtain the dynamic range of the required gain. However, the amplifier of two or more stages increases noise at the transmit output stage. In particular, the increased noise in the receive band can degrade reception sensitivity performance. There are two general methods for mitigating the noise at the transmit output stage. One is to reject the noise in the receive band, and the other is to suppress the noise in the receive band.
The receive band noise at the transmit output stage can be cancelled using a Surface Acoustic Wave (SAW) filter. However, the SAW filter causes gain loss, and additional current is consumed to compensate for the gain loss. When a single transceiver supports multiple bands or multiple modes, the number of the required SAW filters increases. The increased number of the SAW filters increases an area of a terminal Printed Circuit Board (PCB) and Bill of Materials (BOM). Accordingly, the SAW filter is not the best solution for the receive band noise rejection. A desirable method for reducing the current consumption and the BOM is to suppress the noise in the transmit output stage. For doing so, it is necessary to design the RF VGA in a single step. To provide the required gain, amplifier elements can be combined in parallel as shown in FIG. 1.
FIG. 1 illustrates amplifier elements for controlling an RF gain in a wireless transmitter according to the related art.
Referring to FIG. 1, an output of a mixer 110 is input to an array of N amplifier elements 120-1 through 120-N. The gain is controlled by turning the array of N amplifier elements 120-1 through 120-N on and off.
Referring to FIG. 1, the amplifier element 120-1 alone is turned on, and the other amplifier elements 120-2 through 120-N are turned off Since the signal output from the mixer 120 is shared by the input stages of the array of N amplifier elements 120-1 through 120-N, a high-frequency signal output from the mixer 110 is fed as the leakage signal to the other amplifier elements 120-2 through 120-N being turned off. The leakage signal, which is combined with the output of the output element 120-1, affects a final output signal. In particular, when a very small output is required, the amplifier element that is turned off is greater than the amplifier element that is turned off in number and thus a parasitic component is more influential in the final output. That is, the leakage signal can be seriously problematic in the low-level output. Further, when the leakage signal is similar to the normal signal in magnitude, Inner Loop Power Control (ILPC) and gain step accuracy required by the 3G and 4G communication standards cannot be satisfied.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.